1. Field of the Invention
The present invention relates to a magneto-resistive element for recording information with orientation of magnetization and reproducing it with a magneto-resistive effect, and a magnetic thin film memory using it.
2. Related Background Art
The magnetic thin film memory is a solid-state memory without moving parts as in a semiconductor memory, and has such advantages over the semiconductor memory that information is not lost even if the power supply is shut down, that it allows infinite number of repeated rewriting, and that there is no risk for information to be lost when it is radiated by radiation. In recent years, a thin film magnetic memory utilizing the giant magneto-resistive effect particularly attracts attention since it can provide higher output than a magnetic thin film memory which has been proposed and uses an anisotropic magneto-resistive effect. For example, the Journal of the Magnetics Society of Japan, Vol. 20, p.22 (1996) proposed a solid-state memory which was constructed, as shown in FIG. 1, by stacking components consisting of a hard magnetic film HM/non-magnetic film NM/soft magnetic film SM to constitute a memory element. This memory element is provided with a sense line S joined to a metal conductor and a word line W insulated from the sense line S by an insulating film I, and information is written by a magnetic field generated by currents through the word and sense lines. Specifically, as shown in FIGS. 2A to 2D, memory states "0" and "1" are recorded by supplying a current I through the word line W to generate a magnetic field with different orientation depending on difference of a current direction ID, thereby inverting magnetization of the hard magnetic film HM. For example, as shown in FIGS. 2A and 2B, "1" is recorded in the hard magnetic film HM by supplying a positive current to generate a magnetic field toward the right, while, as shown in FIGS. 2C and 2D, "0" is recorded in the hard magnetic film HM by supplying a negative current to generate a magnetic field toward the left. Reading of information is performed by supplying a current I smaller than the recording current through the word line W to invert magnetization of only the soft magnetic film SM, and by measuring variation of resistance in the film. When the giant magneto-resistive effect is utilized, different resistance values are generated in the case where the magnetization of the soft and hard magnetic films SM and HM is parallel and in the case where it is anti-parallel, so that the memory states of "1" and "0" can be determined from variation of resistance in each case. When a positive-to-negative pulse as shown in FIG. 3A is applied, the orientation of the soft magnetic film is changed from right to left, so that its resistance value for the memory state "1" changes from a small value as shown in FIG. 3B to a large value as shown in FIG. 3C, while it for the memory state "0" changes from a large value as shown in FIG. 3D to a small value as shown in FIG. 3E. When the resistance variation is thus read, information recorded in the hard magnetic film HM can be read regardless of the state of magnetization in the soft magnetic film SM after recording, so that non-destructive reading can be attained.
However, in the magnetic thin film memory with the above arrangement, an anti-magnetic field (self-demagnetizing field) generated in the magnetic layer cannot be negligible as the area of bit cell is reduced, so that the magnetization is not fixed in one orientation and becomes unstable for the magnetic layer for holding the record. Therefore, the magnetic thin film memory with the above arrangement has a disadvantage that information cannot be saved when the bit cell is miniaturized, so that it cannot be highly integrated.